This invention is generally related to lifting and hoisting apparatus and, more particularly, apparatus for lifting and positioning aircraft engines during installation.
Wing-mounted engines of large transport airplanes must be periodically removed for servicing and maintenance. Such engines are normally attached to the underside of the airplane wing, or to a pylon depending from the wing, by means of special-purpose attachment assemblies. More specifically, the engine is typically provided with what are known as engine cone bolts, which consist of an upwardly projecting conical member having a threaded stud projecting from its upper end. The upwardly projecting engine cone bolts are received in cooperably shaped, downwardly opening conical bores, which are known as wing-mounting cones and which are formed in structural members of the wing. The threaded studs of the engine cone bolts pass through central apertures in the wing-mounting cones so as to enable the engine to be bolted to the wing, with the conical members of the engine cone bolts and the mating wing-mounting cones operating to distribute stresses and also precisely orient the engine with respect to the wing.
Such an engine is ordinarily installed by lifting it upwardly into position to be secured to the underside of the wing. In doing so, the engine cone bolts must be accurately aligned with and inserted into the corresponding wing-mounting cones. This ordinarily requires that the engine be positioned at a particular angular orientation and lifted directly upwardly while maintained in such orientation so that all of the engine cone bolts and their corresponding wing-mounting cones are brought into alignment and mated simultaneously. Failure to maintain the engine in the proper orientation while raising it into position for mounting can result in damage to the engine cone bolts or the wing-mounting cones. Such damage can arise due to the large mass of the engine, typically on the order of 5000 pounds, and the correspondingly large lifting forces employed, which can fracture or otherwise damage the engine cone bolts or the wing-mounting cones when brought together in imperfect alignment.
Previous methods and apparatus for engine installation have proved unsatisfactory for various reasons. For example, chain hoists have long been used to install airplane engines. Several such hoists are suspended from anchors located on the underside of the airplane wing and are connected to the engine so as to enable the engine to be drawn upwardly into its mounting position. The several hoists are independently operable in order to permit the engine to be brought into its proper angular orientation for mounting. The hoists are usually manually operated in order to prevent excessive and unpredictable force from being applied, such as could be the case with powered chain hoists. One disadvantage of this method of installation is that the number of personnel required makes the process relatively expensive. Also, it is difficult to precisely orchestrate the operation of the several hoists so as to achieve a correct engine orientation and at the same time draw the engine directly upward while so oriented. Further, the method is undesirable from a safety standpoint because the assisting personnel are normally located beneath the overhead suspended engine.
Airplane engines have also been installed with forklifts. This has previously been a common practice in the industry, since the engines are ordinarily supported while removed from the airplane on special-purpose engine dollies that include provisions for lifting with a conventional forklift. Such dollies are designed to support the engine generally in the correct orientation for mounting, so that the engine and dolly can be lifted upwardly as a unit for engine installation with a conventional forklift. Nevertheless, small adjustments to the engine orientation are often required, and such adjustments are difficult or impossible to achieve with a conventional forklift. This problem is exacerbated by the fact that the forklift operator is ordinarily unable to ascertain the upward force exerted by the forklift. Since the weight capacity of a conventional forklift is ordinarily much greater than the weight of an airplane engine, it is an easy matter for the forklift operator to inadvertently raise the engine upwardly against the wing with an excessive amount of force. This can easily result in damage to the attachment members, particularly if excessive upward force is applied while the engine is in an incorrect angular orientation. Such damage has in fact been caused in this manner to essential structural elements of the wing in several instances, and in at least one instance has resulted in catastrophic failure of the engine-mounting pylon during flight. This problem is of particular concern because, in most instances, the forklift operator is unable to determine whether excessive force has been applied, and further because the resulting damage is of a type that is likely to go undetected at the time of engine installation, but which could nevertheless cause catastrophic failure under high load conditions during flight.
Accordingly, it is an object and purpose of the present invention to provide an improved lifting and positioning apparatus for use in the installation of aircraft engines and the like. More particularly, it is an object of the invention to provide a lifting apparatus that is capable of raising an aircraft engine to its mounting position, and which is also capable of providing rotational motion of the engine with three degrees of freedom so as to obtain a desired angular orientation for mounting.
It is a further object of the invention to provide a lifting apparatus for an aircraft engine that is self-limiting in the amount of upward force that may be exerted.
It is yet another object of the invention to provide a lifting apparatus for an aircraft engine that achieves the foregoing objects and purposes and which may also be used in another mode for transportation of an aircraft engine and its associated engine dolly.